Ventajas
Great all around compensation - from salary, benefits (401k & pension & flexible work], medical [fantastic]
Great people - at the company you understand everyone around is came from being one of the smartest people at their previous job/university. Within IT the overwhelming majority of people really care for you, this feels way more collaborative than competitive.
Career Development - lots of opportunities to grow in breadth of experience to get deep in your skills and grow in leadership skills
Desventajas
Work Politics - being such a large corporation with a lot of history there is a tendency to be work politics/red tape sheerly because of the size of the company. However, it is not really bad if you are willing network , put yourself out there to talk with leaders, and be a normal hard-working enjoyable employee. If you do these two things you will succeed at ExxonMobil.